Current-collecting device for small commutating machines

ABSTRACT

A current-collecting device for small commutating machines having a commutator of 85 to 95 percent silver and 15 to 5 percent copper; and having brushes of 50 to 70 percent silver, 25 to 40 percent palladium, and 3 to 10 percent copper.

United States Patent Inventor llenry Kristiansen Sarnen, SwitzerlandAppi. No. 57,964

Filed July 24, 1970 Patented Nov. 2, 1971 Assignee lnterelectrleSeehseln A.G.

Switzerland CURRENT-COLLECTING DEVICE FOR SMALL [56] References CitedUNITED STATES PATENTS 3,191,084 6/1965 Ooka et al. 310/252X 3,171,9973/1965 Hammer..... 310/233 3,310,718 3/1967 Lupfer 252/514 X PrimaryExaminer-Milton O. l-lirshfield Assistant Examiner-B. A. ReynoldsAttorney-Arthur Schwartz ABSTRACT: A current-collecting device for smallcommutating machines having a commutator of 85 to 95 percent silver and15 to 5 percent copper; and having brushes of 50 to 70 percent silver,25 to 40 percent palladium, and 3 to 10 percent copper.

PATENTEDuuv 2 l97l INVENTOR HENRY KRISTIANSEN 'iATTORNEYCURRENT-COLLECTING DEVICE FOR SMALL COMMUTATING MACHINES BACKGROUND ANDOBJECTS The invention relates to a current-collecting device for smallor midget commutating machines comprising a commutator mounted on therotor shaft and stationary brushes brushing on the commutator.

in small commutating machines the problem arises that under ahigh-current load of the current-collecting device the commutator andthe brushes burn away rapidly. The life of high-performance small motorshas thus been very limited hitherto.

Especially in small commutating machines having an ironless armature,which may be constructed for high speeds, an excessively high currentarises during starting in motor operation and this current makes thelife of the machine several times shorter than the life in continuousoperation. It is already known to increase the life by using relativelythick brushes. This has, however, the disadvantage of producingrelatively high frictional losses, thus reducing the efficiency of themicromotor. Moreover, the use of thick brushes results in only arelatively small increase in the life because the thick brushes must beapplied with a relatively high contact pressure, particularly at highspeeds, and this in turn increases the frictional wear of the brushes.

The problem underlying the invention is to produce a current-collectingdevice of the type mentioned at the beginning for small or midgetcommutating machines which has a long life even under a high-currentload.

SUMMARY The solution of this problem resides in that the commutatorconsists of a silver-copper alloy comprising 85 to 95 percent silver and15 to percent copper and that the brushes consist of asilver-palladium-copper alloy comprising 50 to 70 percent silver, 25 to40 percent palladium and 3 to percent copper.

It is admittedly already known to increase the life of acurrent-collecting device by a specific choice of alloys. However, forthis purpose relatively expensive alloys have been used, consisting ofsilver and palladium for the brushes and platinum, iridium or gold,platinum and copper for the commutators.

Preferably, the material of the brushes consists of an alloy of 63percent silver, 32 percent palladium and 5 percent copper and thematerial of the commutator of an alloy of 90 percent silver and 10percent copper. Such a current-collecting device is relativelyinsensitive to high-current loads of the type which can occur moreparticularly in commutating machines having an ironless armature.

To improve the commutating in high-speed machines the brush may becoated at least on its contact surface with a softmetal layer having athickness of 2 to 40 microns. It is advantag'eous for the surfaceroughness of the commutator to be 0.3 to 6 microns and preferably 0.3 to2 microns. Such a current-collecting device may be used with advantagein highspeed machines with a high-current load of the commutator,ensuring long life of the current-collecting device.

DETAILED DESCRIPTION The invention will be described in detail hereafterwith reference to an example of embodiment.

The FIGURE shows a current-collecting or takeoff device comprising acommutator 1 having five segments 2 mounted on an insulating hub 3 whichis fixedly mounted on a shaft 4 carrying the armature. Two brushes 5engage the commutator, only one of these brushes being illustrated. Thebrush is provided with a thin tin coating 6.

The material used for the commutator segments 2 was an alloy of 90percent silver and 10 percent copper and the material used for thebrushes a silver-palladium-copper alloy comprising 63 percent silver, 32percent palladium and 5 percent co er.

The rameter of the commutator was of the order 2 mm.

and each brush consisted of three individual brush leaves having a widthof0.5 mm. and a thickness of 0.1 mm.

For comparison purposes a current-collecting device was made having thesame dimensions as the device according to the invention but havingcommutator segments which consisted in known manner of an alloy of 97percent silver and 3 percent copper and brushes of a gold-silver-copperalloy comprising 70 percent gold, 20 percent silver and 10 percentcopper.

Comparative tests showed that at currents over 0.2 A. the life of thecurrent-collecting device according to the invention was 5 to 10 timesgreater than the life of the known device used for comparison.

The surface of the brushes and/or the commutator segments may be coatedwith a thin soft-metal layer, preferably tin. This considerably reducescommutation faults of the type which arise at high speed, even over longoperating times.

The current-collecting devices according to the invention may be usedboth for direct current and for alternating current machines.

I claim:

1. In a current-collecting device for small commutating machinesincluding a commutator member mounted on a rotor shaft and stationarybrush members contacting the commutator, the improvement comprising:

a. said commutator member being formed of segments of an alloycomprising approximately to 95 percent silver and 15 to 5 percentcopper, and

b. said brush members formed of an alloy comprising 50 to 70 percentsilver, 25 to 40 percent palladium, and 3 to 10 percent copper.

2. A collecting device as defined in claim 1 wherein said brush alloybeing approximately 63 percent silver, 32 percent palladium and 5percent copper.

3. A collecting device as defined in claim 1 wherein said commutatorsegments being of approximately percent silver and 10 percent copper.

4. A collecting device as defined in claim 1 wherein the surface of atleast one of said members having a coating of a layer of soft metalthereon.

5. A collecting device as defined in claim 4 wherein said metal is tin.

6. A collecting device as defined in claim 4 wherein the layer on saidbrush members has a thickness of approximately 2 to 4 microns.

7. A collecting device as defined in claim 1 wherein said commutatormember has a surface roughness of 0.3 to 6 microns.

8. A brush for a motor comprising an alloy of approximately 50 to 70percent silver, 25 to 40 percent palladium and 3 to 10 percent copper.

9. A brush as defined in claim 8 wherein said alloy is approximately 63percent silver, 32 percent palladium, and 5 percent copper.

t s s s s

1. In a current-collecting device for small commutating machinesincluding a commutator member mounted on a rotor shaft and stationarybrush members contacting the commutator, the improvement comprising: a.said commutator member being formed of segments of an alloy comprisingapproximately 85 to 95 percent silver and 15 to 5 percent copper, and b.said brush members formed of an alloy comprising 50 to 70 percentsilver, 25 to 40 percent palladium, and 3 to 10 percent copper.
 2. Acollecting device as defined in claim 1 wherein said brush alloy beingapproximately 63 percent silver, 32 percent palladium and 5 percentcopper.
 3. A collecting device as defined in claim 1 wherein saidcommutator segments being of approximately 90 percent silver and 10percent copper.
 4. A collecting device as defined in claim 1 wherein thesurface of at least one of said members having a coating of a layer ofsoft metal thereon.
 5. A collecting device as defined in claim 4 whereinsaid metal is tin.
 6. A collecting device as defined in claim 4 whereinthe layer on said brush members has a thickness of approximately 2 to 4microns.
 7. A collecting device as defined in claim 1 wherein saidcommutator member has a surface roughness of 0.3 to 6 microns.
 8. Abrush for a motor comprising an alloy of approximately 50 to 70 percentsilver, 25 to 40 percent palladium and 3 to 10 percent copper.
 9. Abrush as defined in claim 8 wherein said alloy is approximately 63percent silver, 32 percent palladium, and 5 percent copper.